This invention relates to improvements in methods of manufacturing polyglycerol esters.
Current methods of manufacturing such esters commence with a fatty acid such as stearic acid, oleic acid and glycerine and use an interrupted two-stage reaction procedure. First, a polycondensation step is performed, the reaction stopped to remove surplus polyglycerol and then esterification is induced.
Thus in order to obtain the desired polyesters, it is necessary that glycerol be subjected to polycondensation by heating same up to 300.degree. C. for 8 to 14 hours prior to esterification of an artificially reduced amount of the polyglycerol so formed with a larger amount of fatty acid. This latter procedure can take up to 10 hours in order to form partial esters of polyglycerols.
The reaction vessel typically used in the manufacture of polyglycerol esters is of the vertical cylinder type and has changed little for many years. It has been found that this reaction vessel produces a surplus of semi-products, typically polyglycerol, and that consequently it is not feasible to perform the above reaction sequence, namely polycondensation and esterification, to produce commercial quantities of polyglycerol esters, and an additional storage vessel for receiving the surplus of semi-product is required. Further, the aforementioned reaction sequence involves cooling the reaction vessel down after condensation to enable removal of the semi-product prior to reheating to commence the esterification process. These deficiencies greatly increase the time required to produce the polyglycerol esters desired and require costly handling and storage facilities coupled with the excessive consumption of energy in reheating the reaction vessel for esterification. Hence the cost of polyglycerol esters in this manner is considerably increased. On the other hand, if condensation is carried out so as to provide merely the aliquot amount of polyglycerol required to achieve the amount of final ester desired in the esterification stage, then polycondensation had to be performed in the lower half of the reaction vessel since only a relatively small amount of glycerine was required. In these circumstances, the kinetics of the reaction, the mass of water vapor formed by the condensation reaction, and the necessity to lift the water vapor from the lower half of the reaction vessel in order to distill out the water vapor, will further extend the reaction time by approximately 50%. This results in undesirable chemical and physical changes in the polyglycerol during the prolonged heating required.
If, on the other hand, condensation is performed utilizing the whole of the volume of the reaction vessel, as is currently the practice, a surplus of polyglycerol is produced and hence additional storage facilities, extra time of 8 to 14 hours in the polycondensation stage and up to 10 hours in the esterification stage is involved, as well as wasting large amounts of heating energy.
Polycondensation is currently conducted under the presence of an alkaline catalyst and expensive fatty acids are currently being used as the raw material for subsequent esterification. Hence, these further disadvantages of the current method in the manufacture of polyglycerol esters demonstrates the need for the present invention.